Terrorists used pressure-cooker bombs, agents say

Death toll at 3; scores suffering grievous injuries

BOSTON — Federal agents zeroed in Tuesday on how the Boston Marathon bombing was carried out — with kitchen pressure cookers packed with explosives, nails and other lethal shrapnel — but said they still didn't know who did it and why.

BOSTON — Federal agents zeroed in Tuesday on how the Boston Marathon bombing was carried out — with kitchen pressure cookers packed with explosives, nails and other lethal shrapnel — but said they still didn't know who did it and why.

The FBI and other law enforcement agencies repeatedly appealed to the public to come forward with photos, videos or anything suspicious they might have seen or heard.

"The range of suspects and motives remains wide open," Richard DesLauriers, FBI agent in charge in Boston, said at a news conference.

He vowed to "go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime."

President Barack Obama branded the attack an act of terrorism but said officials don't know "whether it was planned and executed by a terrorist organization, foreign or domestic, or was the act of a malevolent individual."

Scores of victims of the Boston bombing remained in hospitals, many with grievous injuries, a day after the twin explosions near the marathon's finish line killed three people, wounded more than 170 and reawakened fears of terrorism.

A 9-year-old girl and 10-year-old boy were among 17 victims listed in critical condition.

Heightening jitters in Washington, where security already had been tightened after the bombing, a letter addressed to a senator and poisoned with ricin or a similarly toxic substance was intercepted at a mail facility outside the capital, lawmakers said.

There was no immediate indication the episode was related to the Boston attack. Senate Majority Leader Harry Reid said the letter was sent to Sen. Roger Wicker, R-Miss.

Officials found that the bombs in Boston consisted of explosives put in ordinary, 1.6-gallon pressure cookers, one with shards of metal and ball bearings, the other with nails, according to a person close to the investigation who spoke on condition of anonymity because the probe was still going on.

Both bombs were stuffed into black duffel bags and left on the ground, the person said.

Investigators said they have not yet determined what was used to set off the Boston explosives.

Pressure-cooker explosives have been used in international terrorism, and have been recommended for lone-wolf operatives by al-Qaida's branch in Yemen.

But information on how to make the bombs is readily found online, and U.S. officials said Americans should not rush to judgment in linking the attack to overseas terrorists.

DesLauriers said that there had been no claim of responsibility for the attack.

He urged people to come forward with anything suspicious, such as hearing someone express an interest in explosives or a desire to attack the marathon, seeing someone carrying a dark, heavy bag at the race, or hearing mysterious explosions recently.

"Someone knows who did this," the FBI agent said.

The bombs exploded 10 or more seconds apart, tearing off victims' limbs and spattering streets with blood, instantly turning the festive race into a hellish scene of confusion, horror and heroics.

The blasts killed 8-year-old Martin Richard of Boston, 29-year-old Krystle Campbell of Medford, Mass., and a third victim, identified only as a graduate student from China who was attending Boston University.

Doctors on Tuesday said objects removed from patients were "clearly designed to be projectiles."

"There's no question some of these objects were implanted in the device for the purpose of being exploded when the device went off," Dr. Ron Walls, chairman of emergency medicine at Boston's Brigham and Women's Hospital told the Boston Herald.

"We've removed BB's and we've removed nails from kids. One of the sickest things for me was just to see nails sticking out of a little girl's body," said Dr. David Mooney, director of the trauma center at Boston Children's Hospital.

Obama plans to visit Boston on Thursday to attend an interfaith service in honor of the victims. In the wake of the attack, security was stepped up around the White House and across the country.